ChromiumOS fork by Neverware that is free for single users as well as offers paid support for education.
Ranked in these QuestionsQuestion Ranking
Pro You can try it via bootable USB
Pro Lightweight and fast
This is basically just Chrome OS which already runs on Cheap chrome books. It works well for web browsing and file storage on low end computers.
Con Limited hardware support
There is a list online of about 100 or so computers that officially support Cloud Ready, but it can also work on a laptop not on that list, results may vary.
Con Only really meant for web browsing
To use the software, you need to have a Google account and log in. Because it's meant for web browsing and researching, you won't find software like Steam, Office, Adobe Photoshop, Aftereffects, etc; or even a 3rd party browser other than Google Chrome.
Although there are plenty of alternative web browser online, and in the Chrome Web Store, which is still supported by Chrome OS.